The Veterinary Resources Program, National Center for Research Resources, has established a Watanabe heritable hyperlipidemic (WHHL) rabbit breeding colony as a resource for investigators requiring this animal model for use in human familial hypercholesterolemia caused by a low density lipoprotein receptor defect. The purpose of this project is to evaluate the influence of genotype on the serum cholesterol and triglyceride concentrations of the NIH WHHL rabbits. Blood was collected from WHHL rabbits in 1991 and 1994. The 1991 mean total serum cholesterol and triglyceride concentrations were 828 and 394 mg/dl, respectively. Serum cholesterol and triglyceride values ranged from 310 to 1251 mg/dl and 107 to 959 mg/dl, respectively. The 1994 total serum cholesterol values ranged from 222 to 1356 mg/dl with a mean of 572 mg/dl. Serum triglyceride values ranged from 134 to 1410 mg/dl with a mean of 423 mg/dl. The 1994 decrease in total serum cholesterol is due to lower concentrations in WHHL rabbits one year and older (406 mg/dl) compared to similarly aged rabbits in 1991 (550 mg/dl).